This invention relates to a process for deodorizing smelly exhaust gas containing at least one smelly material selected from the group consisting of acidic smelly materials, such as hydrogen sulfide, mercaptans, dimethyl sulfide, dimethyl disulfide and the like; basic smelly materials, such as ammonia, amines and the like; and smelly organic materials, such as ketones, alcohols, aldehydes, carboxylic acids and the like, which is generated from disposal of human excrements or sewage disposal.
Treatment of such exhaust gas is usually effected in the following steps:
(a) the first step for removing basic components in the gas;
(b) the second step for removing acidic components in the gas with a sodium hypochlorite solution; and
(c) the third step for adsorbing the remaining smelly components in the gas with activated carbon.
The above first step includes (i) a method for washing the exhaust gas by water, (ii) a method for washing exhaust gas with a dilute solution of hydrochloric acid or sulfuric acid, or (iii) a method for washing the exhaust gas with a solution of sodium hypochlorite containing hydrochloric acid and sulfuric acid.
In the above method (i), a large amount of water is necessary for removing water-soluble, basic materials efficiently. Water containing ammoniacal nitrogen, NH.sub.4.sup.+ --N, etc. causes secondary pollution. In the above method (ii), control of concentration of the acidic solution in response to the concentration of the basic components in the exhaust gas is necessary. In the above method (iii), there is possibility of generation of chlorine compounds, which tend to cause secondary pollution. When a solution of sodium hypochlorite with high concentration is used for treating such exhaust gas, excess sodium hypochlorite remains in the solution after contacting the gas. The sodium hypochlorite remaining in the waste solution causes secondary pollution, such as water pollution. In this case, a sodium hypochlorite mist is further entrained in the treated exhaust gas. Such exhaust gas containing sodium hypochlorite mist causes air pollution, since the sodium hypochlorite generates oxidant, such as atomic oxygen. When the exhaust gas containing the sodium hypochlorite mist is washed with water, it is necessary to further treat the washing water to make it harmless.